A device of this kind is described for example in European Pateint EP-0 318 629, which relates to a pressure generator which is suitable in particular for the hydraulic actuation of the clutches of automobile vehicles.
When a hydraulic pressure generator is used as a master cylinder for the clutch of an automobile vehicle, the axial vibration of the drive shaft, connected to the clutch assembly, gives rise to mechanics and hydraulics vibrations which are transmitted through the clutch slave cylinder to the master cylinder and consequently to the pedal, producing a disagreeable sensation for the driver.
Although the patent cited above specifically has as an object to propose means for reducing these vibrations, and even though the device described in this patent does indeed have significant qualities from this point of view, the characteristic curve of the output pressure produced by the device against the displacement of the piston assembly has a region of non linearity which is undesirable in certain particular circumstances.